Estimate, one of the best horses ever owned by the Queen, could have run her last race after trailing home last behind Cavalryman in the Artemis Goodwood Cup.

Nine days after making global headlines when it emerged she was one of seven horses to test positive to Morphine – a case linked to contaminated feed which means she will be disqualified from her second place in the Ascot Gold Cup in June – the Sir Michael Stoute-trained mare appeared ill-at-ease on Goodwood’s gradients and never looked like justifying her position as 2-1 favourite.

It was a second career defeat at the track, with Estimate having finished third in the 2012 Lily Langtree Stakes.

Disappointing: Estimate (centre) comes right at the back of the pack despite being 2-1 favourite at Goodwood

It is understood Estimate was one of the runners in the Goodwood Cup line-up subject to a post-race dope test.

Given the back-drop to the race, the BHA had little option but to include her in their testing programme but it was entirely a cosmetic but necessary procedure to head off any conspiracy theorists.

With running options now thin on the ground, retirement is now a big option. That would be a sad end to a career for a mare who gave her owner one of her most joyous days on a racecourse with victory in the 2013 Ascot Gold Cup.

Certainly plans for an exciting potential swansong in Australia’s Melbourne Cup in November look certain to be shelved.

Stoute said: ‘Ryan said she wasn’t letting herself down and I wasn’t happy from a long way out.’

While royal racing adviser John Warren added: ‘Ryan said she felt uncomfortable. He even wondered whether she was in season but Michael didn’t think so. Probably the track doesn’t suit her.

‘It is complicated now. We were hopeful that if she did well today(Thursday) that we would be brave enough to go to the Irish St Leger to sharpen her up and see if she had enough toe for Melbourne. Now we are back to the drawing board.

‘The option are so limited. We will have to get our heads around it and see what the Queen thinks.’

Owner: The Queen stands with Estimate in the winner's enclosure at Ascot after Gold Cup victory

A second shot at the Melbourne Cup – he finished 12th in 2012 – is a possibility for Godolphin-owned Cavalryman, who finished a neck in front of Saeed Bin Suroor-trained stablemate Ahzeemah.

Third, four and a half lengths further back in a race run at an uneven tempo, was Michael Ownen-owned 2013 winner Brown Panther.

At the age of eight, Cavalryman is enjoying a resurgent season having won a group three race in Dubai in March and the Group Two Princess Of Wales’s Stakes at Newmarket last month.

But his jockey Kieran Fallon fears he will now be weighted out of Australia’s biggest contest.

He said: ‘All our good horses go over there and get killed by the handicapper while the best Australian horses get in light.’

Definitely retired is Michael Winter-trained Missunited. The Irish mare, who was third in the Ascot Gold Cup, sustained a suspensory ligament injury when bravely winning the Lily Langtree Stakes under Jim Crowley.

A sense of excitement swept the track when it emerged film star Tom Cruise was a guest of Goodwood’s owner Lord March.

He generated a frenzy of attention when presenting model Edie Campbell with her prize for winning the charity Magnolia Cup.

Cruise is best known for his Mission Impossible films and trainer Richard Hannon must have felt that finding a winner was getting that way after five seconds on the opening two days.

But the tide turned as his two-year-olds Shagah and Ivawood scored under Richard Hughes.

The latter, an impressive four and a half length winner of the Group Two Richmond Stakes, could now step up to group one class in the Prix Morny. He is 8-1 favourite for the 2015 2,000 Guineas with Ladbrokes.